Fagan et al1 followed up a group of 61 normal elderly individuals (Clinical Dementia Rating [CDR] 0, ≥60 years old) for a mean time of 3 to 4 years to study cognitive decline. Individuals who progressed during the follow-up from a CDR of 0 to a CDR of 0.5 or higher were defined as converters toward very mild or mild dementia. All the other subjects were considered nonconverters. A cutoff value of 0.214 or greater for the ratio of cerebrospinal fluid (CSF) phosphorylated tau181/β-amyloid42 (ptau181/Aβ42) at baseline was adopted to predict converters and nonconverters at follow-up. The authors' conclusion is that, “CSF tau/Aβ42 ratios show strong promise as antecedent (preclinical) biomarkers that predict future dementia in cognitively normal older adults.”